Figure 1.

Genetic interactions of skb1 with genes encoding key mitotic regulators in S. pombe. (A) The skb1 null mutation partially suppresses the t.s. growth defect of the cdc25–22 mutant. cdc25–22 and cdc25–22 skb1Δ S. pombe strains were streaked on YEA plates and incubated at either 36°C (Top) or 33°C (Bottom). The cdc25–22 skb1Δ mutant strain produced visible colonies at 36°C, whereas the cdc25–22 strain did not. At 33°C, the cdc25–22 skb1Δ strain grew significantly faster than the cdc25–22 mutant. (B) Overexpression of skb1 exacerbates the cdc25–22 t.s. growth defect. The cdc25–22 mutant was transformed with a plasmid for overexpression of skb1 (pREP1Skb1) or with a control plasmid (pREP1). Transformants were streaked onto EMM plates and were assayed for growth at 30°C (Top) or 33°C (Bottom). Overexpression of skb1 retarded the growth of the cdc25–22 mutant at 30°C and completely inhibited growth at 33°C. (C) cdc25–22 pREP1- and pREP1Skb1-transformed cells were grown at 26°C in liquid EMM to a density of about 10⁶ cells per ml then shifted to either 33°C or 36°C and incubated for 5 hr before 4′,6-diamidino-2-phenylindole (DAPI) staining and microscopic analysis to determine the percentage of binucleated and septated cells in each culture. (D) skb1 overexpression is inhibitory to the growth of cdc2–3w cdc25Δ, but not cdc2–3w cells. pREP1- and pREP1Skb1-transformed cdc2–3w cells (Top) and cdc2–3w cdc25Δ cells (Bottom) were assayed for growth by being streaked on EMM plates and incubated at 30°C. (E) pREP1- and pREP1Skb1-transformed wild-type cells (CHP428) were streaked onto EMM and grown at either 30°C (Top) or 36°C (Bottom). (F) skb1 overexpression inhibits growth of the wee1Δ mutant at 36°C. pREP1- and pREP1Skb1-transformed wee1Δ cells were streaked onto EMM and grown at either 30°C (Top) or 36°C (Bottom).